Gadgetopia

The way I see it, it's just a convenient way to check for input parameters. You can do that with PHP 4 too, only it requires much more code:

function doSomething($param1, $param2) {
    if (!is_array($param1)) trigger_error('Error!', E_USER_ERROR);
    if (!is_a($param2, 'MyClass')) trigger_error('Error!', E_USER_ERROR);
    ...
}

instead of

function doSomething(array $param1, MyClass $param2) {
    ...
}

I agree that this is an innocent first step, but it's really the first thing PHP has ever done in terms of typing. I bet future versions will let you type hint for string and numeric as well. How far beyond that is a config switch to strongly type the whole shindig?